Actually, it's pretty hard to get an honest opinion most places.
Most people say something nice no matter how bad it is. That really doesn't help us get better or make changes for the better.
I tend to just not say anything if I think something is bad. after all, my opinion isn't worth that much anyway.
However if you ASK for it, I'm not shy about making suggestions. I do try to make them in a positive way though.
As Diki says though, if you post a song for all the world to see, you will get criticism, usually both good and bad.
I didn't comment on this performance mainly because the guy said he was "just practicing".
DonM